The “Odd Couple” of Spiral Galaxies
The dazzling pair of galaxies M81 and M82, intertwined in dramatic gravitational one-step, are a rewarding sight for northern stargazers with small telescopes. The pair is visible for most of the year but swing into optimum viewing position over the next few months. And today, you get first viewing of a brand-new image of this galaxy pair from a dedicated amateur astrophotographer.
M81 and M82 could be called the “odd couple” of galaxies. They are gravitational roommates, but they have totally different personalities. M81 is the brighter and larger of the two galaxies, an elegant spiral with clearly visible gossamer arms extending continuously around the core. Galaxies with such near-perfect shape are called “grand-design” spirals. At magnitude 6.8, M81 is easily visible as a bright smudge in binoculars or small scope, though the spiral shape is discernible only in larger telescopes or time-exposure images.
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A newly processed image M81 and M82 (courtesy of Terry Hancock at Down Under Observatory); click to enlarge.
By contrast, the nearby M82 is a mangled wreck of a galaxy. Fainter, at magnitude 8.4, it’s a ragged cigar-shaped edge-on spiral in the process of blowing itself to bits. At one time, astronomers thought M82 was exploding for a reason that defied explanation. Now it’s believed it was a normal spiral galaxy racked by an intense bout of star formation in its core, likely triggered by a strong gravitational interaction with M81 about 100 million years ago. In infrared light, M82 is the brightest galaxy in the sky, likely because of intense star formation in its spiral arms.
You can find this odd couple off the bowl of the Big Dipper by following a diagonal line from the star Phad through Dubhe (see image below). The pair, also called Bode’s Nebulae after their discover, lie about 7 degrees on this diagonal past Dubhe. The two are a little more than half a degree apart. You can see both together in a wide field eyepiece; their difference in size, shape and brightness are easy to discern. But you’ll need clear dark skies and a good-sized scope to see the spiral structure in M81.
The location of M81 and M82 (a.k.a. Bode’s Nebulae) off the bowl of the Big Dipper in the far-northern skies, as seen looking north-east at mid-northern latitudes at about 9 p.m. local time (click to enlarge).
The centers of M81 and M82 are now only 150,000 light years apart, and they continue to interact strongly. As they move closer, M82 may eventually be stripped of gas and dust and become a tight and featureless elliptical galaxy.
A bit of trivia: only one supernova has been detected in M81. On March 28, 1993, the Spanish amateur Francisco Garcia Diaz discovered the exploding star from Lugo, Spain. He discovered the 11th magnitude supernova the old-fashioned way… visually… with his 10-inch Newtonian telescope at a magnification of 111x.
